The present invention is directed to fiber optical transport systems. More particularly, the invention provides a method and system for an integrated optical receiver for reducing the size and cost of optical transport systems. Merely by way of example, the invention has been applied to dense wavelength division multiplexing (DWDM) optical transport systems employing InP photodetectors. But it would be recognized that the invention has a much broader range of applicability.
Since its first deployment in the middle of 1990s, dense wavelength division multiplexing (DWDM) has become a dominant technology for long haul and regional backbone transport networks, and is gradually making its way to metro area networks. An optical transport system usually includes one or more linecards. A linecard is often built around one or several optical components. For example, the received DWDM optical signal from the transmission fiber is first passed through a demultiplexer linecard, which includes DMUX filters. A commonly used DMUX filter is based on arrayed waveguide grating (AWG) made of silica-on-silicon. The optical outputs from the demultiplexer linecard, each at a wavelength by the ITU-T standards, are then fed into the receiver linecards. The optical connections between the linecards are generally made through optical fibers. A receiver card typically includes a photodetector, for example, a p-i-n (PIN) photodiode, or an avalanche photodiode (APD), that converts the input optical into an electrical signal for further processing. The photodetector chips inside the photodetector packages are typically made of InP semiconductor compounds.
Even though these conventional DWDM systems are useful in some areas, they have many limitations that restrict their effectiveness in broader applications. Some of these limitations are discussed below, and then improved techniques based on embodiments of the present invention are presented.